The present invention is one related to a method and equipment for implementing a storage function in a passive optical network system and which, in concrete terms, by utilizing a storage device installed in an optical network unit within the passive optical network system, stores data making exclusive use of a comparatively wide bandwidth such as e.g. audiovisual data, and transfers the data stored in the aforementioned storage device to the user.
Since a Passive Optical Network (PON) has advantages like long distance capability, wide bandwidth, and low cost, it is already used as one of the most effective methods for end users connected to a network. A passive optical network system has an extended structure of the tree type or the like. FIG. 12 is a structural drawing of a basic passive optical network with current technology. As shown in FIG. 12, there are included in a PON system an optical line terminal (OLT) 100, an optical distribution network (ODN) 120, and multiple optical network units (ONU) 140, and the like, and the system is capable of provide services such as voice and audiovisual communications between an end user 150 and a core network 102.
ITU-T Recommendation G.983 recommends letting a PON system have a point-to-multipoint extended structure, making it pass through a passive optical distribution network between an OLT and a plurality of ONUs, and connecting it to e.g. an optical splitter. Different transfer methods are used for data transfers in the uplink and downlink directions within a PON, a broadcast method being used in the downlink direction, i.e. in the direction from the OLT to each ONU, since there are normally no restrictions with respect to bandwidth allocation in the downlink direction, i.e. the direction from the OLT to the ONUs, but as for the uplink direction from the ONUs to the OLT, an allocation of the bandwidth becomes necessary in order to avoid collisions and congestion.
As shown in FIG. 12, the data in the downlink direction from OLT 100 to ONU 140 are transferred with a broadcast method via an optical splitter 109 inside ODN 120 to each ONU in the downlink direction. Subsequently, through an analysis of the original data, each ONU receives the data affiliated with its own data.
In actual applied processes, the downlink bandwidth in the downlink direction of the PON system has been recognized to be generally very limited, at 155.52 Mbps, 622.08 Mbps, 1.25 Gbps, and 2.4 Gbps. Since there is not any restriction with respect to the allocation of bandwidth for the downlink direction, the downlink bandwidth is shared by all ONUs, so for this reason, the downlink flow of this system becomes very big and there exist problems such as flow congestion and data delays. Normally, the major portion of the downlink bandwidth is used exclusively by audiovisual services such as Internet Protocol Television (IPTV), IPTV groupcast services being particularly notable. Transferring the same audiovisual contents at different times to users with different ONUs can be said to a kind of waste from the perspective of the network as a whole.
In order to solve the aforementioned problem, precisely audiovisual data are stored in locally distributed audiovisual servers installed between the core network and the connection networks, one method of which is presented in Patent Reference U.S. Pat. No. 5,550,577. To put it concretely, one video on demand network (VODN) transfers, based on a control signal sent from a user, audiovisual information to the user. In order to reduce duplication expenses of the audiovisual information, there is a need for this video on demand network to maintain one extremely big audiovisual database in a central audiovisual server, and if comparatively popular audiovisual data are stored in a locally distributed audiovisual server, it is possible for the locally distributed audiovisual server to provide direct audiovisual information to the user by proceeding in this way.
However, the method presented in Patent Reference U.S. Pat. No. 5,550,577A can only solve the problem of bandwidth waste in the core network portion of the downlink bandwidth and is unable to solve the problem of bandwidth waste in the connection network (such as PON) portion of the downlink bandwidth.
Currently, the problems mentioned hereinafter exist in PON systems.
1. In case data making exclusive use of a comparatively wide bandwidth such as unicast data and big data packages are transferred with a PON system, it is only possible for the user of a designated ONU to receive data. In case the user of a different ONU requires the same data, these data are sent from an IPTV server to reach the user via the entire PON system, and in this case, the result is that the same data makes exclusive use of the downlink bandwidth of the PON system multiple times, leading to a kind of serious waste of the bandwidth resource.
2. Due to the fact that audiovisual data for groupcast method transfers occupy a comparatively wide bandwidth and a different ONU user can only receive the data at the same time, he cannot view these data (e.g. viewing an audiovisual program) at a different time. In other words, in case a markedly different ONU user wants to view the same program at a different time, there is a need to access the IPTV server multiple times, the result being that exclusive use is made of the downlink bandwidth multiple times, leading to serious waste of the bandwidth resource.